HIGH-CONCENTRATION BORON-DIFFUSION IN SILICON - SIMULATION OF THE PRECIPITATION PHENOMENA

An extensive investigation on the diffusion of boron implanted at high concentration in preamorphized silicon has been carried out for rapid thermal annealing and conventional furnace annealing. The rapid process of epitaxial regrowth of the amorphous layer brings B atoms into substitutional positions, and thus electrically active, up to a concentration threshold of about 3.5×1020 cm-3. This value is nearly independent of the annealing temperature and of the implanted dose. Since the concentration of dopant in solution is higher than the solubility value, precipitation phenomena occur in concomitance to diffusion during the annealing. The kinetics of precipitation has been investigated at 800, 900, and 1000 °C with isothermal treatments ranging between 10 s and 171 h. A simulation program taking into account precipitation phenomena has been developed modifying the suprem iii code. The density of nuclei of the new phase has been evaluated on the base of the models of classic nucleation theory, while the rate of precipitation growth has been determined following Ham's theory. Excellent agreement with experimental data has been obtained in a wide range of experimental conditions. The model represents a significative improvement of the simulation of high-concentration B diffusion in Si; the more commonly used process simulations are inadequate to correctly foresee the dopant redistribution in supersaturated conditions.